Intestinal consumption of intravenously administered fuels

Total parenteral nutrition has been extensively used to feed patients with a variety of gastrointestinal diseases, but little attention has focused on the nutritional requirements of the gut. To investigate intestinal consumption of intravenously administered nutrients, uptake of three principal fuels determined from in vitro studies was quantitated in seven awake, unrestrained dogs. Portal blood flow was measured by a dye dilution technique and, simultaneously, substrate samples were obtained from chronic indwelling arterial and portal venous catheters. Studies were performed during a postabsorptive basal period and during separate infusions of glutamine (0.10 mmol/kg X min), glucose (0.10 mmol/kg X min), and beta-hydroxybutyrate, (0.40 mmol/kg X min). During the basal period there was a significant arterial-portal vein gradient for glucose (144 +/- 26 mumol/liter) and glutamine (49 +/- 11 mumol/liter). These substances were taken up by the gut at rates of 4.11 +/- 1.23 and 1.43 +/- 0.19 mumol/kg X min, respectively. No significant uptake of beta-hydroxybutyrate was determined in the basal studies (0.27 +/- 0.10 mumol/kg X min). During substrate infusion, gut glucose uptake was unchanged (2.68 +/- 1.67 mumol/kg X min, NS), but consumption of glutamine (4.60 +/- 0.66 mumol/kg X min, p less than 0.001) and beta-hydroxybutyrate (4.33 +/- 0.71 mumol/kg X min, p less than 0.001) increased significantly. During parenteral feedings in patients with gastrointestinal disorders, circulating levels of beta-hydroxybutyrate and glutamine are often low, and glutamine is absent from standard amino acid solutions. Current parenteral formulation may not provide appropriate fuels for the gastrointestinal tract.